Radiolarian biostratigraphy of Ilot Brun and Denouel Quarry sections, New Caledonia

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Pascher, K.M.; Hollis, C.J. 2017 Radiolarian biostratigraphy of Ilot Brun and Denouel Quarry sections, New Caledonia. Lower Hutt, N.Z.: GNS Science. GNS Science report 2017/34 23 p.; doi: 10.21420/G2DS61


Abstract: Fossil radiolarian assemblages were studied from two outcrops in New Caledonia, the Denouel Quarry and Ilôt Brun sections on Nouméa Peninsula, to determine the age of the composite succession. The radiolarian assemblages are poorly to moderately preserved and of variable abundance and diversity. Samples of the lower Denouel section (up to 4.21 m), which is composed of a massive micritic limestone containing chert nodules in the basal part, are barren of radiolarians or exhibit only rare to few specimens. Assemblages in the upper Denouel section (4.51–13.65 m) contain abundant radiolarians, whereas the lower Ilôt Brun section (0–1.78 m) contains few to common radiolarians. Most of the latter section (2–21 m) is either barren of radiolarians or contains only rare radiolarian fragments. The radiolarian-rich interval in the upper Denouel section might be due to higher nutrient (e.g. silica, iron) availability in the water column, and the successive decline in radiolarians throughout the Ilôt Brun section may be related to climatic or other environmental changes. Lithological changes throughout the Ilôt Brun section, from a micritic limestone at the base towards a pink-red calciturbidite at the top, may indicate changing environmental or depositional conditions. The radiolarian assemblages in both sections can be described as subtropical, containing less tropical species than typically occur at low-latitude sites. The assemblages contain more tropical species than sites further south (e.g. DSDP Site 277 and Mead Stream, onshore New Zealand). Primary marker species of the low-latitude radiolarian zonation are rare and sporadic in their distribution (e.g., Theocotyle cryptocephala and Dictyoprora mongolfieri) or absent (e.g., Eusyringium lagena). Therefore, secondary marker species have mainly been used to correlate the composite section to low-latitude radiolarian zones RP9 to RP11, corresponding to an age range of ~50 to ~45.3 Ma. (auth)